1. Field of the Invention
The present invention relates generally to damage tolerant aluminum alloys, and in particular, to such alloys useful in the aerospace industry suitable for use in lower wing skin applications and as fuselage skin.
2. Description of Related Art
Materials particularly adapted for use in lower wing skin applications including 2×24 alloys are generally known, as described, for example, in U.S. Pat. Nos. 5,213,639 and 6,444,058 as well as in the PCT application WO 99/31287, the content of which is incorporated herein by reference in their entireties. Damage tolerance of 2×24 alloys is of particular importance and materials that have excellent properties in this regard are highly desirable. These 2×24 alloys, derived from the chemical composition of the 2024 alloy, usually contain manganese in a concentration of at least 0.15 to 0.20%, and up to 0.8 or 0.9%. This is the case of the 2×24 alloys which have been standardized by The Aluminum Association (AA): 2024, 2024A, 2124, 2224, 2224A, 2324, 2424, 2524.
European Patent Application EP 1 170 394 A discloses methods for manufacturing damage tolerant AlCuMg sheet. These methods involve unusual (hot cross rolling) or otherwise expensive manufacturing steps (repeated intermediate heat treatment) in order to obtain a precisely controlled microstructure.